Combination Interferon-α2a and 13-cis-Retinoic Acid Enhances Radiosensitization of Human Malignant Glioma Cells in Vitro1
- The Cell Biology Laboratory of the Patty and George Hoag Cancer Center, Newport Beach, California 92658
Abstract
We investigated the individual and combined effects of cis-retinoic acid (CRA) and/or IFN-α (IFN) and/or radiation therapy (RT) against a human glioma cell line (American Type Culture Collection; U373MG) to evaluate the possible radiosensitization properties of these agents in vitro. Glioma cells were incubated for 24 h in 96-well plates (2 × 102 cells/well) in standard culture medium. Sets of U373 (n = 12) were exposed to CRA (3 × 106 μm), IFN (25 units/ml), CRA plus IFN, or standard culture medium. After an additional 24 h of incubation, the U373 cells were subjected to increasing radiation doses (up to 16 Gy). Glioma cells were harvested 92 h after irradiation, and cell survival curves were determined from [3H]thymidine incorporation data (over the last 24 h). The experiment was repeated for both the untreated control group and the combined CRA/IFN group. To verify the [3H]thymidine assays, a clonogenic assay was also performed. Single cell suspensions of U373 cells were plated out in six-well plates (n = 3). After chemical and RT treatment, colonies of 50 cells or more were counted, and cell survival curves were generated as fractions of nonirradiated controls. The amount of RT (in Gy) that would cause a 50% survival fraction (lethal dose 50 or LD50) was calculated from the survival curves by regression analysis. The following LD50s were obtained: <$REFLINK> The results showed that for both the [3H]thymidine incorporation assay and the clonogenic assay, the combination of IFN/CRA rendered U373 cells more susceptible to ionizing radiation than the untreated control or either single agent alone.
Footnotes
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 This work was supported by the Hoag Hospital Foundation. Portions of this work were presented in abstract form at the 88th meeting of the American Association for Cancer Research, San Diego, California, 1997, and the 12th meeting of the Society of Biological Therapy, Pasadena, California, 1997.
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↵2 To whom requests for reprints should be addressed, at the Office of the Medical Director, Hoag Cancer Center, One Hoag Drive, Building 41, Newport Beach, CA 92658. Phone: (949) 760-2091; Fax: (949) 760-2102; E-mail: rdillman{at}hoaghospital.org
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↵3 The abbreviations used are: CRA, cis-retinoic acid; IFN, interferon-α2a; RT, radiation therapy.
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- Accepted November 30, 1998.
- Received August 20, 1998.
- Revision received November 23, 1998.
